Various powders exemplified by white and colored pigments such as titanium oxide, zinc oxide, red iron oxide, and the like and extender pigments such as mica, sericite, and the like are widely used in the fields of base cosmetic compositions and other various cosmetic compositions such as sunscreens, nail colors, nail coats, foundations, mascaras, eye liners, and the like. However, untreated powder is prone to agglomerate due to the electric charge and polarity, trace amounts of impurities, and the like on the powder surface. Therefore, powders that have been subject to various surface treatments are widely used for the purpose of enhancing dispersibility and stability of a powder in a cosmetic composition and also improving the tactile sensation, moisture resistance, sebum resistance, and the like of a cosmetic composition comprising a powder.
Known examples of such surface treatments include lipophilization treatments using an oil agent, a metal soap, or the like; hydrophilization treatments using a surfactant, a water-soluble polymer, or the like; hydrophobization treatments using silicone compounds; silica treatments; alumina treatments; and the like. Particularly, in recent years, there have been many cases where a surface treatment using a silicone compound having a reactive moiety in the molecule has been performed. The reactive moiety forms a chemical bond with the powder surface and, as a result, the surface treatment using the silicone compound is effective from the perspective of simultaneously modifying the surface of the powder and blocking the surface activity of the powder without significantly altering the characteristics of the powder itself. Additionally, because surface treatment can be thoroughly performed, the treatment agent will not separate from the powder surface, even when compounded in a cosmetic composition comprising a solvent. An example of such a surface treatment is a method in which a powder is surface treated using a methylhydrogenpolysiloxane (Patent Document 1). However, in this method, unreacted Si—H groups still remain even after the surface treating of the powder and, therefore, there is a problem when this powder is compounded in a cosmetic composition because hydrogen gas may be produced depending on the components and the like in the cosmetic composition.
On the other hand, methods for manufacturing a powder dispersion using a hydrophilic modified organopolysiloxane that has good compatibility with the powder surface have been proposed. Examples thereof include a method for forming a polyether-modified organopolysiloxane into a powder dispersing aid (Patent Document 2) and a method for forming an organopolysiloxane modified by polyglycerine or a similar polyhydric alcohol into a powder dispersing aid (Patent Document 3). However, there are problems in that the powder dispersion effectiveness is still insufficient, viscosity of a power dispersion obtained by dispersing a powder in silicone oil or a similar oil agent increases gradually over time, fluidity is lost, and the like.
As a method to solve the problems described above, the present applicant has proposed methods using a co-modified organopolysiloxane copolymer having a group that has a carbosiloxy dendron structure and a glycerin derivative, polyhydric alcohol, or similar hydrophilic group in the molecule (Patent Documents 4, 5, and 6). Such co-modified organopolysiloxanes are safe and do not produce hydrogen, and can be advantageously used in the surface treating of a powder. Moreover, affinity with other raw materials of cosmetic compositions is superior, and the dispersibility and stability of the powder in a cosmetic composition comprising a powder can be enhanced.
Generally, in some instances, formulations principally comprising silicone as an oil agent tend to have excessively light tactile sensation due to the characteristics of the silicone. However, to meet a broad range of consumer needs, cosmetic compositions having different tactile sensations need to be prepared and, particularly, in order to provide a feeling of luxury, formulations that deliver a tactile sensation with weight are preferable. Additionally, regarding the preparation of such systems, the development of formulations comprising oil agents other than silicone (e.g. isododecane, various hydrocarbon solvents, and the like) has also been actively investigated. However, with the co-modified organopolysiloxane described above, there has been a problem in that the desired dispersibility in the hydrocarbon solvent cannot be achieved because molecular design is carried out with silicone-based formulations principally in mind. Thus, there is a pressing need for the development of a dispersing agent and a silicone-based activating agent that is soluble in a hydrocarbon solvent.
Patent Document 7 describes an alkyl-modified silicone polyether that is also cost-efficient as a solution to the problems described above. This co-modified organopolysiloxane copolymer is mainly used as an emulsifier but is also used as a dispersing agent and is applied to various types of powder cosmetic compositions. However, these copolymers all have comparatively high molecular weights and a large number of hydrophilic groups, leading to the problem of dispersibility in microparticulate powders being poor or the problem of stickiness occurring when added to the formulation. On the other hand, in the case that the molecular weight is too small, it will become hard to work as an emulsifier and keep an emulsion composition stable. Therefore, these documents substantially fail to disclose or suggest a silicone surfactant having both emulsification capability for emulsifiers and surface treating capability for powder-dispersant.